1. Field of the Invention
The present invention relates generally to computer add-on devices and, more particularly, to an easily installable, removable, self-contained mass storage device for use with a computer having a bus system accessible through an aperture in the computer housing.
2. Description of Related Art
Most modern computers include an internal bus having a plurality of multisignal receptacles for insertion of various add-on circuit cards having conductive edge or connector terminals. Add-on or plug-in circuit cards provide the computer with such features as additional memory, IEEE 488 interface, a modem interface, and extra serial or parallel I/O ports.
Many computers include a housing defined above a substantially flat base having an upwardly-extending back wall and front wall and below a removable cover comprised of a top wall having two downwardly-extending side walls. An example of such a computer is any one of the so-called PC compatibles found in nearly any office. The base of such a computer supports the multisignal receptacles, add-on cards, and other components, such as a power supply, floppy disks, hard disks, etc., within the interior of the housing.
In the past several years, mass storage devices, such as hard disks, have become commonplace as both original and add-on equipment for computers of all types. A hard disk, used to store and retrieve large quantities of digital information, is generally comprised of a plurality of record-like platters having a magnetic coating and a plurality of read/write heads for reading and writing digital information on the platters. External contaminants such as smoke and dust can destroy a hard disk because the read/write heads float extremely near to the platter surfaces being rotated at high speed. Because of this concern, hard disks are provided in hermetically sealed canisters that include the necessary electronics and interface connections to allow external control of hard disk operations.
A controller card is also needed to operate a hard disk. The controller card provides an electronic interface between the computer bus system and the hard disk in one of five common disk interface types: IDE; ESDI (Enhanced Small Device Interface); SCSI (Small Computer System Interface); ST-506; and ST-412. In general, the controller card is an add-on circuit card that plugs into the bus system and is therefore physically separate from the hard disk. Power and I/O cabling are provided between the controller card and the remote hard disk, which may be located inside or outside of the computer housing.
In a conventional computer having an internal bus system, the installation of a hard disk and controller card is relatively permanent and is a labor intensive and time consuming process. Installation typically requires removal and replacement of the cover and the numerous fasteners that attach the cover to the base. With the cover off, the controller card is installed by pressing its edge connector into an empty multisignal receptacle (a "slot"), the hard disk is mounted onto or adjacent the base with screws or straps, or both, and the necessary power and I/O cabling is connected between the controller card and the hard disk. The cover and fasteners are then replaced.
Many companies must take security precautions with information considered to be proprietary or vital to national security. Such information can, of course, be stored in various types of computer storage media, including hard disks, floppy disks, and tape drives. With floppy disks and tape drives, the storage medium may be easily removed and secured when not in use. However, the same removal process is not possible with the just-described conventional hard disks, since they are permanently mounted in the interior of the computer housing. Because of the generally fixed nature of hard disks, sensitive information is frequently stored on removable floppy disks, while other non-sensitive information is stored on the hard disk. This is very inefficient. Also, floppy disks have limited storage capacity and their access speed and transfer rate are very slow relative to hard disks.
One approach to simplifying the task of hard disk installation is set forth in U.S. Pat. No. 4,639,863, issued to Harrison et al. on Jan. 27, 1987. Harrison et al. offer an add-on circuit card that contains both a controller and a hard disk. Although the apparatus of the '863 Patent simplifies and speeds up the installation of a hard disk in a computer having an internal bus system, it is not designed for, nor is it suitable for day-to-day removal and replacement. In particular, the apparatus of the '863 Patent is undesirable for removal and replacement because the user must remove and replace the computer cover to gain access to the card, and because the controller circuitry is exposed and subject to static damage if handled.
Other removable media devices are available, such as those that utilize the 51/4-inch peripheral bay. The SyQuest Model SQ555 is an example of such a device. The limitation of all such devices that utilize a 51/4-inch mounting bay is that they require significant disassembly of the typical computer system for installation. Another limitation of these particular devices is storage capacity. Typical removable cartridge capacity is about 44 Mbytes as compared to half a Gbyte or more for hard disks.
Some computer manufacturers, such as HEWLETT-PACKARD, offer a computer having an enclosure wherein the multisignal receptacles of a bus system are accessible through an aperture provided in an exterior wall of the enclosure. The present inventor calls this type of bus system an externally accessible bus system because add-on circuit cards may be inserted and removed from the interior of the computer without having to remove a cover or disassemble the computer to any extent.
In a computer having such an externally accessible bus system, the standard hard disk is conventionally mounted permanently inside of the computer housing. This arrangement is undesirable because an internal, permanently mounted hard disk is difficult and time consuming to install and obviously not readily removable. Upgrading, replacing, or removing (e.g., for security) such a device is an impractical and laborious task.
Free standing external hard disks may also be connected to such a computer system. With an external hard disk, an interface card (e.g., a SCSI card) is installed in the externally accessible bus system and a cable is connected between the external hard disk and I/0 signals on the interface card. The free standing external hard disks are undesirable as well, because such devices typically require a substantial amount of desk space or rack space if the computer is in a rack and are usually too bulky and cumbersome to be readily placed in a safe for secure keeping.